Apple Final Cut Express HD - Manual (Page 976)

976 Part XII Output
More About Compression Markers
Compression markers identify areas of abrupt change in your sequence, such as a cut
from a black room to a bright grassy plain. Compression markers are automatically
inserted by Final Cut Express HD at all edit points. You can also place compression
markers where you want; these are forced compression markers. When a movie or
sequence is exported with compression markers, the exported QuickTime movie has an
extra text track, in addition to the video, audio, and timecode tracks.
Note: Compression markers have no effect on iDVD projects.
Some video compression applications, including Compressor, are capable of using
information in the compression track of your movie to optimize the placement of
I-frames during the process of MPEG-2 compression to achieve maximum playback
quality. By correctly identifying cuts, transitions, and gaps in your sequence, you can
avoid compression artifacts in these areas of your final movie on DVD. See “
About the
MPEG Format ” on page 973 for more information about I-frames.
In most cases, the compression markers that are placed automatically by
Final Cut Express HD will suffice. However, in areas of abrupt visual change that take
place inside a clip with no edit point to give it away, a user-placed compression marker
can help to compress that section more smoothly. For example, suppose you have a
shot that contains an extremely fast 180-degree pan from a jungle scene to the beach
behind the camera. This rapid change has no cut point for Final Cut Express HD to
detect automatically. But if you manually place compression markers at frames in this
clip occurring immediately before and after the pan, compression applications such as
Compressor will know to place I-frames at those points in the compressed video to
minimize any compression artifacts.
A compression marker is distinguished by the text <COMPRESSION> appearing in the
Comment field of its Edit Marker window. For details on adding and deleting markers,
see “
Using Markers ” on page 235.
Compression markers will export differently depending on whether you’re exporting a
sequence or a clip.
 If you’re exporting a clip: You must place compression markers in the clip for a
compression track to be created.
 If you’re exporting an edited sequence: Final Cut Express HD exports compression
markers for each cut, transition, and gap that appears in your sequence, in addition
to any compression markers that you added manually to the sequence. Compression
markers added to individual clips are ignored.